1a. Objectives (from AD-416):
1. Determine if sap flow (‘bleeding’) is a prerequisite for budbreak and canopy development.
2. Test if spring shoot vigor and fruit set are related to soil moisture before or during budbreak.
3. Develop practical recommendations for early-season irrigation management.

1b. Approach (from AD-416):
We propose to investigate with pot and field experiments designed to vary soil moisture before and during budbreak. The resulting differences in grapevine vigor will be assessed by measuring shoot length and final pruning weight. Measurements of bleeding sap volume and composition will enable us to determine whether spring shoot vigor is related to the bleeding rate and/or content. Such measurements will be supplemented with estimates of fruit set, yield formation and fruit composition. We will then use the knowledge gained from these experiments to develop practical recommendations for early-season vineyard management. Documents Grant with Washington State University

3. Progress Report:
This research was conducted in support of NP305 objective 1 "Determine effects of water manageemnt on wine grape productivity and fruit maturity" of the parent project. Dry winters may result in stunted shoot growth and poor fruit set in grapevines. We hypothesized that this may be caused by the vines’ inability to initiate sufficient sap flow (bleeding) before budbreak; failure of the hydraulic system might be responsible for inadequate water supply to the developing canopy. Preliminary studies were conducted and a potted vine trial was conducted to understand the correlation between soil moisture level and vine growth and development in sandy loam and loamy sand soil maintained at moisture levels from permanent wilting point (PWP) to field capacity (FC). The resulting differences in bud break and grape vine vigor were assessed by measuring shoot length. Bleeding sap was collected for multiple times to determine whether spring shoot vigor is related to bleeding rate and or its content. In support of our hypothesis, the data collected provide evidence that soil moisture affects sap flow rate, vine vigor, and fruit set. Vines maintained at PWP did not survive. Bringing PWP vines close to FC after three weeks saved the vines; however, many inflorescences aborted. Soil moisture below about 2% above PWP inhibited sap flow, which was directly associated with an inability of the buds to break. Sap flow, shoot vigor, canopy development, leaf photosynthesis, and fruit set increased with increased soil moisture to a maximum at 3-4% below FC.